The present invention pertains to tool assemblies adapted to perform a work operation on a web of moving material, and more particularly to tool assemblies of the type wherein a pair of opposed tool means are mounted for movement to and from each other to periodically engage and release a web of material to perform a work operation on it. Typically, such work operation is a punching operation in which the paired tool means are, respectively, a punch and a die. However, other work operations such as embossing and printing are equally well carried out by such tool assemblies.
U.S. Pat. No. 3,861,260 entitled Double Bucket Die Cutting Assembly issued to the assignee of the present application shows a tool assembly of this type wherein a die bucket and punch bucket are mounted eccentrically on mounting means carried by a frame to perform die punching on a web of material moving between them. The eccentric mounting on the rotating mounting means provides a periodic orbiting action which intermittently brings the two buckets into work performing contact with the web moving between them.
Web materials are fed to such tool assemblies, often at high speeds of web travel for repeated die punching or other work operations on the web. Obviously, the repeat distance between work operations on the web, e.g., between die punches, is determined by the frequency of the periodic movement of the tool means and the web velocity. If it is desired to be able to select different repeat distances it is necessary to either vary the frequency of tool movement or the average web speed or both. It is impractical to attempt to vary the average web speed. Generally, maximum web speed is desired for increased production. Further, web materials have a tendency to stretch and/or bunch up with changes in web velocity. Also, the tool assembly is usually one of a series of operations being carried out on the moving web and other pieces of equipment both upstream and downstream of the tool assembly require a constant overall web velocity so that proper registration between different operations may be maintained, etc.
Varying the frequency of periodic tool movement also causes certain problems. The tool means must have a tangential velocity which is substantially equal to the web velocity at the time of engaging the web. That is, the tool, i.e., that portion thereof which engages the web material, must move with the web at about the same speed as the web during engagement or else the tool will tear the web. Prior art attempts to deal with this problem usually involve accelerating and decelerating the tool means by means of clutches, eccentric gears or the like so that the tool means is slowed or speeded up as necessary at the time of engagement to match the web speed. The average tool means velocity must be maintained so that the tool completes its cycle and repeats the work operation at the desired repeat distance for a given constant average web velocity. Such acceleration and deceleration devices are cumbersome, complicated and expensive. The acceleration and deceleration forces impose strains on the equipment and require special mounting and shock absorbing means.
It is accordingly an object of the present invention to provide a novel and improved tool assembly in which the period of frequency of tool means engagement with the web, i.e., the repeat distance between tool work operations on the web, may be varied without necessity of speeding up or slowing down the tool means drive.
It is another object of the present invention to provide a tool assembly in which web velocity passing between the tool means is periodically increased and decreased and synchronized with the movement of the tool means while maintaining the through put web velocity constant in order to match tool means tangential velocity to the momentary web velocity at the time of engagement of the tool means with the web.
It is a further object of the present invention to provide a novel tool assembly in which stretching and/or buckling of the web means upstream or downstream of the tool assembly is precluded while web velocity through the tool means is reciprocatingly increased and decreased.
Yet another object of the present invention is to provide a novel tool assembly wherein a moving web of material is fed between a first and second opposed tool means defining a work station between them and guide members are employed to engage the moving web both before and after the work station with the guide means being simultaneously reciprocated to alternately increase and decrease the distance along the web path of travel from the guide member before the work station to the work station to alternately decrease and increase the momentary velocity of the web through the work station.
Other objects and advantages of the invention will become apparent from the following description.